A new study provides evidence that the lingering effects of hallucinogenic drugs, known as Hallucinogen Persisting Perception Disorder (HPPD), are more common among users than previously understood. The study, which focused on two types of HPPD, found that while the more severe form is relatively rare, a milder form affects a significant portion of hallucinogen users. The findings have been published in the Journal of Psychoactive Drugs.
The study was motivated by a desire to understand the prevalence and impact of HPPD, a condition characterized by persistent visual disturbances reminiscent of the effects of hallucinogenic drugs, even after cessation of drug use. Researchers aimed to explore the nature of HPPD, which is broadly categorized into two types. Type I includes brief, often pleasant visual experiences, while Type II involves prolonged and distressing symptoms that can impede daily functioning.
The study also sought to investigate the neurological basis of HPPD, its correlation with personality traits like neuroticism, and its connection to various hallucinogenic and non-hallucinogenic drugs.
“We felt that HPPD could be an under-recognised and under-reported phenomenon and wanted to collect some data on how common it was in users of psychedelic and non-psychedelic drugs,” said study author James Stone, a professor of psychiatry at the Brighton and Sussex Medical School.
To gather data, the researchers posted advertisements on Reddit, targeting subreddits where discussions about drug use were prevalent. The study recruited participants who were over 18 and had a history of hallucinogen use. The initial pool of respondents totaled 802, but after applying strict criteria for attention and completeness of responses, the final sample consisted of 415 individuals.
Participants were asked to fill out a consent form and a questionnaire assessing their neuroticism using a standardized tool known as Goldberg’s Big Five Inventory. The questionnaire also inquired about their drug use history, including types of drugs, dosages, and frequency. To understand their experience of HPPD, questions were asked about the nature, intensity, and duration of their visual hallucinations. The survey also probed into other psychological disorders they might have and their habits regarding drug testing.
About 39.7% of the participants fell into the category of Type I HPPD, experiencing milder symptoms, while 4.3% were categorized as having Type II HPPD, indicating more severe and intrusive symptoms. The most commonly reported symptom was false perceptions of movement.
“The more severe type of HPPD (type II) appears to occur in around 4-5% of hallucinogen users, while fleeting and non-intrusive hallucinogenic experiences following hallucinogen use are more common,” Stone said. “We were surprised that such a large proportion of respondents (over 40%) reported at least some HPPD symptoms.”
Interestingly, only four participants reported having received a formal diagnosis of HPPD, highlighting a potential gap in clinical recognition of the disorder.
In terms of psychological traits, the study found no significant difference in neuroticism across the two types of HPPD. However, the prevalence of anxiety-related symptoms was notably higher in individuals with Type II HPPD. This group was also more likely to report additional psychological issues like obsessive thoughts, paranoia, and panic attacks. The study further revealed that the use of certain drugs, notably 25I-NBOMe, dextromethorphan, nitrous oxide, and benzodiazepines, was more common among those with Type II HPPD.
Despite these insights, the study faced several limitations. Firstly, the high rate of incomplete questionnaires reduced the overall data pool. Secondly, the use of Reddit for recruitment might have introduced a bias towards users with extreme experiences of drug use. Additionally, the reliance on self-report questionnaires raises questions about the accuracy of the reported experiences and symptoms.
“This was a small online questionnaire study,” Stone explained. “We were not able to formally diagnose respondents – only to classify their symptoms as more or less likely to be type I or type II HPPD. It is potentially affected by selection bias as we surveyed users of Reddit only (although excluding specific HPPD subreddits), and participation in the study was voluntary.”
Looking to the future, researchers suggest a need for larger sample sizes to mitigate the high attrition rates. They also emphasize the importance of developing more precise diagnostic criteria for HPPD, tailored to differentiate between its subtypes. This would not only aid in better clinical recognition and treatment of HPPD but also allow for more accurate research into the psychobiology of the disorder.
The study, “Association of Hallucinogen Persisting Perception Disorder with Trait Neuroticism and Mental Health Symptoms“, was authored by Morgan Hadley, Alicia Halliday, and James M. Stone.